Thanks for reaching out to us and welcome to the community! I can definitely understand the frustration when it comes to wiring issues as it can be very confusing to figure out sometimes, but I'm happy to look into this for you.
It's possible that your B and C wires are for your heat pump and common wire, or are proprietary under your original HVAC system, which might make it incompatible with Nest Thermostats. Due to this setup, it's strongly recommended that a Nest pro helps you install your thermostat. However, since we might not know the specifics of your HVAC system, I suggest using the Compatibility Checker to double-check if your system is compatible with our thermostats. For your own reference, using this article to help identify the different wires can be helpful when consulting HVAC installation services.
Please let me know if you have any more questions or concerns as I'm happy to help.
-From Garrett DS, Community Specialist.
